An electromagnetic launcher, or railgun, uses very high electrical current (on the order of millions of Amperes) to create an electromagnetic force, or Lorentz force, to accelerate projectiles. A simple rail gun is made of two parallel metal conductor rails (hence the name railgun) that are connected to an electrical power supply.
Electrical current is supplied from a positive terminal of the power supply to one of the conductor rails. The electrical current flows from the conductor rail through an electrically conductive projectile (that serves as an armature) across the bore of the rail gun to the other conductor rail and returns to a negative terminal of the power supply.
The flow of electrical current makes the railgun act like an electromagnet. To that end, a powerful magnetic field is created in the region of the rails up to the position of the projectile. In accordance with the right-hand rule, the created magnetic field circulates around each conductor. Because the electrical current flows in opposite directions along each rail, the net magnetic field between the rails is directed vertically. In combination with the electrical current flowing across the projectile (armature), a Lorentz force is produced which accelerates the projectile along the rails. Other forces acting on the rails attempt to push the rails apart. However, because the rails are firmly mounted, they cannot move. As a result, the projectile is able to slide along the rails away from the end with the power supply.
If a very large power supply (on the order of around a million Amperes of electrical current or so) is used, then the force on the projectile will be tremendous. By the time the projectile leaves the ends of the rails (that is, the muzzle), the projectile can be travelling at speeds on the order of several kilometers per second.
However, practical applications of electromagnetic launchers in the field typically encounter several issues. These issues include: (1) maintaining electrical contact during launcher recoil; (2) providing a fast rise in the launch forces for optimal acceleration profile (especially for rotating machine pulsed power supplies); and (3) providing a balanced assembly to facilitate launcher aiming.
Regarding the first issue, as does a conventional propellant gun, an electromagnetic launcher recoils during a launch event. Recoil forces are usually absorbed by springs and viscous dampers. However, in an electromagnetic launcher, electrical contact for very high electrical current (again, on the order of millions of Amperes) must be maintained during launcher recoil motion.
In the laboratory, electromagnetic launchers may attempt to maintain electrical contact during recoil in a number of ways. For example, stiff mounts may be used to prevent significant motion, massive launchers may be used to minimize motion, a coaxial brush arrangement may be located near the rearmost point of the launcher, and multiple, large coaxial or twisted cables may be used to provide a flexible connection.
The first three approaches are not practical for field applications where launcher mobility and aiming are necessary. Moreover, coaxial or twisted cables require large volumes to achieve adequate flexibility due to the large cable sizes and number of cables required. In addition, coaxial or twisted cables are difficult to cool when multiple launches are required during a short time.
Regarding the second issue, in order to take full advantage of electromagnetic launcher configurations, it is desired that the acceleration profile in the bore be nearly constant. In typical, known railguns, this requires very fast rise times for the current. Such fast rise times are especially difficult to achieve when rotating machines (that is, electrical generators) are used for the pulsed power supply.
In an attempt to achieve higher acceleration levels at lower current levels, augmented electromagnetic launchers have been developed. Augmented electromagnetic launchers reduce the current required to flow through the projectile body by using multiple current conductors in the launcher to augment the magnetic field with which the armature current interacts. Because these augmenting turns have been employed over the full length of the launcher, the need remains for fast current rise to maintain nearly constant acceleration, although the peak current levels needed are reduced. This reduction in current level is achieved at the expense of higher inductance electromagnetic launcher configurations, longer resistive paths for current flow, and higher residual energy stored in the magnetic field after launch. When the projectile exits an electromagnetic launcher, the magnetic field (that has stored residual energy) collapses and current continues to flow. The energy stored in the magnetic field is either dissipated in a large arc or contributes to inefficiency through component heating in a muzzle shunt, even if energy recovery techniques are employed. Because greater energy is stored in an augmented launcher, the losses are correspondingly greater, overall system efficiency is reduced, and cooling requirements are increased.
Augmentation can provide an advantage early in the launch by requiring a less demanding current rise rate for a pulsed power supply. However, the increased overall inductance requires a greater peak energy transfer during the entire launch. Therefore, an overall greater demand is placed upon the pulsed power supply.
Regarding the third issue, conventional propellant guns achieve a center of gravity (CG) closer to the breech than the muzzle because the high pressure following propellant ignition and subsequent lower pressures during launch and blow-down result in a tapered barrel configuration with massive breech assemblies. However, electromagnetic launcher forces are more uniform and do not lend themselves to tapered configurations in simple launchers. As a result, conventional electromagnetic launcher configurations are balanced about the mid-length of the launcher rather than toward the breech. Therefore, in developing a fielded platform difficult trades must be made between trunnion placement, swept volume on the platform interior, and aiming forces.
The foregoing examples of related art and limitations associated therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.